1. Field of the Invention
The present invention relates to an organic electrolysis reactor for performing an electrolytic oxidation reaction. More particularly, the present invention is concerned with an organic electrolysis reactor for performing an electrolytic oxidation reaction of a system comprising a substrate and a reductant, comprising: a casing; an anode which comprises an anode active material and which is ion-conductive or active species-conductive; a cathode which comprises a cathode active material and which is ion-conductive or active species-conductive; and means for applying a voltage between the anode and the cathode, wherein the means for applying a voltage is disposed in the outside of the casing and connected to the anode and the cathode, wherein the anode and the cathode are disposed in spaced relationship in the casing to partition the inside of the casing into an intermediate compartment between the anode and the cathode, and an anode compartment on the outside of the anode.
By using the organic electrolysis reactor of the present invention to perform an electrolytic oxidation reaction, such as an electrolytic carbonylation reaction, various useful chemical compounds, for example a carbonic diester, can be produced efficiently, safely and stably, with high selectivity under moderate conditions.
The organic electrolysis reactor of the present invention can solve the various problems of a non-electrolytic oxidation reaction which is performed by using a catalyst, i.e., the problems that a deterioration of a catalyst occurs, that the selectivity for and yield of a desired product become low, that complicated operations are necessary, and that a large amount of energy is consumed.
For example, when the production of a carbonic diester from carbon monoxide and an alcohol by an electrolytic carbonylation reaction is performed by using the organic electrolysis reactor of the present invention, there can be obtained advantages not only in that the carbonic diester can be produced efficiently, with high selectivity and at low cost under moderate conditions, but also in that the reactor of the present invention can solve the various problems of the conventional methods for producing a carbonic diester, such as the problems that the use of phosgene (which is poisonous) is necessary, that a corrosion of a reactor by a by-produced chlorine-containing compound occurs, that a deterioration of a catalyst occurs, that there occurs formation of a dangerous, explosive mixture of a starting material with oxygen, and that the selectivity for and yield of a desired carbonic diester become low.
The organic electrolysis reactor of the present invention can be used not only for performing an electrolytic carbonylation reaction, but also for performing electrolytic oxidation reactions other than an electrolytic carbonylation reaction, such as oxidation of an alkane, oxidation of an alcohol, epoxidation of an olefin, oxidation of a benzylic site, oxidation of an allylic site, oxidation of an aromatic ring of an aromatic hydrocarbon, oxidation of a sulfur compound and oxidation of a nitrogen compound. In addition, the organic electrolysis reactor of the present invention can also be used for performing an oxidative addition reaction by electrolysis, with respect to such a type of oxidative addition reaction as conventionally, usually performed by a non-electrolytic method.
The present invention is also concerned with a method for producing a chemical compound by performing an electrolytic oxidation reaction, using the organic electrolysis reactor mentioned above.
2. Prior Art
There are an extremely wide variety of oxidation reactions. One of such oxidation reactions is an electrolytic oxidation reaction.
An oxidation reaction using an electrolysis can be performed as follows. An anode and a cathode are placed in an electrolyte solution containing a substance to be oxidized. A voltage is applied between the anode and the cathode to thereby electrolyze the substance, so that the substance is oxidized at the anode. Such an oxidation reaction using an electrolysis is called an xe2x80x9celectrolytic oxidation reactionxe2x80x9d. In some cases, an oxidation reaction which hardly proceeds under ordinary reaction conditions not utilizing an electrolysis can easily proceed by electrolytic oxidation. Therefore, the electrolytic oxidation reaction is extremely useful.
The electrolytic oxidation is applicable to an extremely wide variety of oxidation reactions, such as oxidation of an alkane, oxidation of an alcohol, epoxidation of an olefin, oxidation of a benzylic site, oxidation of an allylic site, oxidation of an aromatic ring of an aromatic hydrocarbon, oxidation of a sulfur compound, and oxidation of a nitrogen compound.
Further, the electrolytic oxidation reaction is also applicable to oxidation reactions which are collectively referred to as the xe2x80x9coxidative addition reaction xe2x80x9d and which are usually performed by a non-electrolytic method. Examples of such oxidative addition reactions include the Wacker reaction for the synthesis of an aldehyde and a ketone from an olefin, acetoxylation, oxychlorination or oxycyanation of an olefin or an aromatic hydrocarbon, a coupling reaction of an olefin or an aromatic hydrocarbon, and a reaction for the synthesis of an ester from an alcohol (see, for example, xe2x80x9cShokubai Koza Vol. 8, (Kogyo Shokubai Hannohen 2), Kogyo Shokubai Hanno I (Lecture on Catalysts Vol. 8 (Commercial Catalytic Reactions No. 2), Commercial Catalytic Reactions I)xe2x80x9d, edited by Japan Catalyst Society, p. 196, 1985, Japan). Furthermore, the electrolytic oxidation reaction is also applicable to a carbon monoxide insertion reaction (carbonylation reaction), which is a variant of the oxidative addition reaction.
Hereinbelow, an explanation will be made with respect to the prior art of the production of a chemical compound by the electrolytic oxidation reaction, taking the carbonylation reaction as an example.
In general, for overcoming a thermodynamic disadvantage, a carbonylation reaction is performed in the presence of oxygen while by-producing water. Such an ordinary carbonylation reaction which is performed without utilizing an electrolysis is represented by the following formula:
Rxe2x80x94H+Rxe2x80x2xe2x80x94H+CO+1/2O2xe2x86x92Rxe2x80x94COxe2x80x94Rxe2x80x2+H2O.
That is, the carbonylation reaction is a reaction performed by subjecting two molecules of substrates each having a hydrogen atom (Rxe2x80x94H and Rxe2x80x2xe2x80x94H) and carbon monoxide to condensation in the presence of oxygen to thereby produce a condensation product while liberating hydrogen and converting the liberated hydrogen (hydrogen ions) into water.
The carbonylation reaction is generally performed by using a catalyst. Examples of such catalysts include the elements of the Groups 8, 9, 10 and 11 of the Periodic Table, such as palladium, and compounds of these elements.
As a substrate (Rxe2x80x94H and/or Rxe2x80x2xe2x80x94H), a wide variety of compounds can be used. Examples of substrates include organic compounds, such as an olefin (e.g. a polyene, such as a diene), an alcohol, an aromatic compound; and inorganic compounds, such as water. The substrates, Rxe2x80x94H and Rxe2x80x2xe2x80x94H, may be the same or different.
As examples of carbonylation reactions, there can be mentioned a reaction for the synthesis of an unsaturated carboxylic acid from an olefin and water, a reaction for the synthesis of an unsaturated ester from an olefin and an alcohol, a reaction for the synthesis of a dialkyl carbonate and a dialkyl oxalate from an alcohol, a reaction for the synthesis of a diaryl carbonate from phenol, and a reaction for the synthesis of a urea analogue and an oxalic diamide (oxamide) from an amine (see, for example, xe2x80x9cShokubai Koza Vol. 9 (Kogyo Shokubai Hanno-hen 3), Kogyo Shokubai Hanno II (Lecture on Catalysts Vol. 9 (Commercial Catalytic Reactions No. 3), Commercial Catalytic Reactions II)xe2x80x9d, edited by Japan Catalyst Society, p. 31, 1985, Japan).
The carbonylation reactions, which can be used to produce useful chemical compounds efficiently, are of great use in the chemical industry. However, the carbonylation reactions frequently pose problems, for example, in that a lowering of a catalyst activity occurs, that a corrosion of a reactor occurs due to the formation of a corrosive by-product derived from a catalyst, that a large amount of energy is consumed due to the use of high reaction temperature and high reaction pressure, that a danger of explosion is present due to the occurrence of a mixing of a starting material with oxygen or a mixing of a reaction product with oxygen, and that the selectivity for and yield of a desired compound are low.
Hereinbelow, these problems of the carbonylation reactions are specifically explained, taking as an example a reaction for the synthesis of a carbonic diester from an alcohol.
A carbonic diester is a useful compound, which is used as an additive for a gasoline and as a raw material for producing carbonates, carbamates, urethanes, and precision chemical compounds, such as pharmaceuticals and pesticides.
Examples of conventional methods for producing a carbonic diester include:
(I) a method in which phosgene is reacted with an alcohol in the presence of a base (see, for example, U.S. Pat. Nos. 2,787,631 and 4,335,051),
(II) a method in which an alcohol is reacted with carbon monoxide in the liquid phase in the presence of oxygen and copper(I) chloride as a catalyst (see, for example, U.S. Pat. Nos. 4,218,391 and 4,318,862),
(III) a method in which an alcohol is reacted with carbon monoxide in the presence of oxygen and a catalyst comprising a compound of an element of the platinum group, such as a palladium compound, and a copper compound, such as copper chloride (or a catalyst comprising a compound of a platinum group element, an alkali metal salt and copper(II) chloride) (see Examined Japanese Patent Application Publication No. 61-8816), and
(IV) a method in which an alcohol is reacted with carbon monoxide in the gaseous phase in the presence of oxygen and a solid catalyst which is obtained by having copper chloride and an alkali metal compound (or an alkaline earth metal compound) carried on an activated carbon (see U.S. Pat. No. 5,004,827).
The commercial production of a carbonic diester has conventionally been conducted by using the method (I) above, since the method (I) has an economic advantage. However, the method (I) is disadvantageous from the viewpoint of safety, since the method (I) has a great defect in that it is necessary to use phosgene (which is poisonous) as a raw material. Further, the method (I) poses a problem that hydrogen chloride (which is highly corrosive) is by-produced during the reaction.
Therefore, as methods which do not use phosgene, the methods (II) to (IV) above have been proposed in which an alcohol is reacted with carbon monoxide in the presence of a catalyst and oxygen to thereby produce a carbonic diester. Since these methods do not use phosgene, prevention of environmental pollution and waste disposal can be simply conducted, so that the entire process becomes simple. Also, the cost of these methods has reached a level which can compete with the cost of the phosgene method. However, these methods (II) to (IV) still have many problems.
For example, the method (II) has the problem that a corrosion of a reactor occurs due to a by-produced, chlorine-containing compound. Therefore, in this method, it is necessary for the inside of the reactor to have a glass lining or an enamel lining, so that it becomes difficult to increase the size of the reactor.
Further, in this method (II), a high concentration of a catalyst and a high partial pressure of carbon monoxide are needed to achieve a satisfactory reaction rate. However, in this method, carbon dioxide is by-produced, and the by-produced carbon dioxide must be purged from the reaction system, and the purging of carbon dioxide inevitably causes a large loss of carbon monoxide and, hence, a lowering of the carbon monoxide partial pressure. Therefore, it becomes difficult to achieve a satisfactory reaction rate.
Further, because the method (II) uses, as a catalyst, a copper salt, which hardly dissolves in an organic solvent, the reaction system becomes a slurry (i.e., a liquid phase containing solids dispersed therein), and the produced carbonic diester is contained in the liquid phase. Therefore, this method has a defect in that it is necessary to perform additional steps for separating the produced carbonic diester from the solids by, for example, membrane separation or centrifugation separation.
In the method (III), the catalyst activity is higher than the catalyst activity achieved in the method (II). Therefore, in the method (III), the catalyst concentration and the carbon monoxide partial pressure need not be very high, as compared to the case of the method (II). However, this method has a problem in that a copper compound as an auxiliary catalyst is converted to a copper oxide, which is precipitated, and, also, by-produced water (by-produced when a carbonic diester is formed) converts the above-mentioned copper compound to a basic copper chloride, which is precipitated, so that it becomes difficult to produce a carbonic diester continuously and stably.
In the method (IV), which employs a gaseous phase reaction using a solid catalyst, the problem of the occurrence of a corrosive by-product, which problem accompanies a liquid phase reaction, can be avoided. However, the method (IV) has problems in that the catalyst activity becomes unsatisfactory, and that the catalyst activity becomes unstable since an insoluble metal compound, such as a basic copper chloride, is precipitated on the solid catalyst due to the presence of water which is by-produced. Thus, with this method, a carbonic diester cannot be produced stably and in high yield for a long time.
Further, the method (IV) uses a mixture of an alcohol, which is flammable, carbon monoxide and oxygen, and such a mixture is explosive, posing a problem from the viewpoint of safety.
For solving the above-mentioned problems, i.e., the problems that a lowering of a catalyst activity occurs, a corrosive by-product is formed, and the use of an explosive mixture is necessary, there have been proposed methods for producing a carbonic diester from an alcohol and carbon monoxide by an electrolytic reaction.
As mentioned above, the carbonylation reaction is thermodynamically disadvantageous, but can be performed relatively easily by utilizing an electrolysis. The carbonylation reaction performed by an electrolytic oxidation is represented by the following formula:
xe2x80x83Rxe2x80x94H+Rxe2x80x2xe2x80x94H+COxe2x86x92Rxe2x80x94COxe2x80x94Rxe2x80x2+H2.
In the electrolytic carbonylation reaction, two molecules of substrates each having a hydrogen atom (Rxe2x80x94H and Rxe2x80x2xe2x80x94H) and carbon monoxide are subjected to condensation while liberating hydrogen. In this method, the liberated hydrogen is not converted to water and, therefore, molecular hydrogen is by-produced.
The electrolytic oxidation reaction for producing a carbonic diester is represented by the following formula:
Rxe2x80x94OH+Rxe2x80x2xe2x80x94OH+COxe2x86x92ROxe2x80x94COxe2x80x94ORxe2x80x2+H2.
Recently, the organic electrolysis reaction has attracted attention as a clean, chemical reaction technique which has high energy efficiency and which can utilize various resources. Therefore, remarkable progresses have been made in the technology for the synthesis of a chemical compound by using the organic electrolysis reaction. Specifically, various reaction techniques have been developed, for example, a membraneless electrolysis method, an anode reaction, a cathode reaction, an electrolysis method using a cation exchange membrane or anion exchange membrane, an emulsion electrolysis method, and a two-liquid-phase electrolysis method. Further, the electrolysis cells have been improved, and the improvement has enabled development of many reactions exhibiting high selectivity.
Examples of methods for producing a carbonic diester by an electrolytic reaction (electrolytic carbonylation method) include:
(V) a method in which electrolytic carbonylation of an alcohol is performed by using a halogen compound as an electrolyte (see J. Electro. Chem. Soc., 125 (12), 1954-1959, 1978, U.S.A.), and
(VI) a method in which gaseous phase electrolytic carbonylation of an alcohol is performed by using an anode containing palladium chloride or copper(II) chloride (see, for example, Electrochimica Acta, Vol. 39, No. 14, 2109, 1994, Switzerland; J. Electro. Chem. Soc., 142 (1), 130-135, 1995, U.S.A.; and Unexamined Japanese Patent Application Laid-Open Specification No. 6-73582).
However, the method (V) above has a problem in that, for obtaining a carbonic diester in high yield and with high current efficiency, the reaction needs to be performed under a carbon monoxide pressure as high as 100 atm., so that the use of a reactor which can stand very high pressure is needed, and it is necessary to perform circulation of a high pressure gas. Therefore, this method is unsuitable for commercial practice.
The method (VI) was proposed by the present inventors. Specifically, the method (VI) is performed as follows. A reactor is provided comprising an electrolysis cell, a diaphragm containing an electrolyte solution, an anode containing palladium chloride or copper(II) chloride, and a cathode containing platinum black, wherein the diaphragm is disposed in the electrolysis cell to partition the cell into an anode compartment and a cathode compartment, and wherein the anode and the cathode are, respectively, disposed in the anode compartment and the cathode compartment. In operation, a voltage is applied between the anode and the cathode while introducing an alcohol and carbon monoxide to the anode compartment and introducing oxygen gas to the cathode compartment, thereby producing a carbonic diester.
The method (VI) has advantages in that it is free from the problems of a lowering of a catalyst activity and a corrosion of a reactor, and that, since oxygen is separated from an alcohol and carbon monoxide by a diaphragm disposed therebetween, formation of an explosive mixture can be prevented, thereby decreasing the danger of explosion. However, this method has a defect in that the selectivity for and yield of the carbonic diester obtained are low.
As apparent from the above, no method has conventionally been proposed which can be used for producing various compounds (e.g., a carbonic diester) efficiently, stably and safely by an electrolytic oxidation reaction (e.g., an electrolytic carbonylation reaction). Also, no reactor has conventionally been proposed which can exhibit an excellent performance when used for producing a compound by an electrolytic oxidation reaction.
In this situation, the present inventors have made extensive and intensive studies with a view toward developing a reactor for producing various chemical compounds (e.g., a carbonic diester) efficiently, stably and safely by an electrolytic oxidation reaction (e.g., an electrolytic carbonylation reaction). As a result, it has unexpectedly been found that various chemical compounds (e.g., a carbonic diester) can be produced efficiently, stably and safely by performing an electrolytic oxidation reaction (e.g., an electrolytic carbonylation reaction) by using an organic electrolysis reactor for performing an electrolytic oxidation reaction of a system comprising a substrate and a reductant, wherein the organic electrolysis reactor comprises: a casing; an anode which comprises an anode active material and which is ion-conductive or active species-conductive; a cathode which comprises a cathode active material and which is ion-conductive or active species-conductive; and means for applying a voltage between the anode and the cathode, wherein the means for applying a voltage is disposed in the outside of the casing and connected to the anode and the cathode, wherein the anode and the cathode are disposed in spaced relationship in the casing to partition the inside of the casing into an intermediate compartment between the anode and the cathode, and an anode compartment on the outside of the anode, and wherein the intermediate compartment has an inlet for an electrolyte solution and a substrate, and the anode compartment has an inlet for a reductant. The present invention has been completed, based on this novel finding.
Accordingly, it is an object of the present invention to provide an organic electrolysis reactor for producing various chemical compounds (e.g., a carbonic diester) efficiently, stably and safely by an electrolytic oxidation reaction (e.g., an electrolytic carbonylation reaction).
It is another object of the present invention to provide a method for producing a chemical compound by using the above-mentioned organic electrolysis reactor.
The foregoing and other objects, features and advantages of the present invention will be apparent from the following detailed description and appended claims taken in connection with the accompanying drawings.